> Right now I have been asked to spec up a system designed to deliver an
> urgent message to several thousand
> subscribers in the shortest possible time. Those who get the message
> late are annoyed that others saw it earlier...

I would not think several thousand emails high enough volume to warrent a
complicated HA system, .. seems like a decent MTA like PostFix or qMail
with current h'w (maybe Opteron) would be more than sufficient?

Seems also that 'Net latency would be a far bigger issue with delivery time
than generating emails - fat pipes on the sending end doesn't guarantee
unbounded traffic capability all the way to the destination.